Chromium-titanium base alloys resistant to high temperatures



United States Patent 3,131,059 CHRUll/HUM-THANIUM BASE ALLGYS RESETANTT0 HEGH TEMPERATWS William T. Ka'arieia, Fort Worth, Tern, assignor toGeneral Dynamics Corporation, San Diego, Calif a corporation of DelawareNo Drawing. Filed Sept. 13, 1961, Ser. No. 137,723 17 Claims. (Cl.75-134) This invention relates in general to alloys capable of resistinghigh temperatures and more particularly, to alloys of such characterwell suited for the brazing of columbium and columbium base alloys andhaving additional utility as high temperature protective coatings and ascasting alloys.

It has become increasingly important, particularly in aircraftapplications, to use materials which are capable of withstandingextremely high temperatures. One such material is columbium, which is arefractory metal possessing a melting point in the vicinity of 4400 F.From a design standpoint, it is an excellent material because of itshigh strength to weight ratio in the 2000 to 2500 F. range of servicetemperatures. It does not strain-harden rapidly, allowing cold workingup to 99% without anneal ing, and it is therefore particularly suitablefor the forming of parts of complex shape. Columbium is alsocharacterized by moderate density (comparable to iron and nickel), and ahigh melting point, with good strength retention above the useful rangeof currently available alloys.

Useful though it is in high temperature areas, joinder of the metal andits alloys presents problems. Thus, although it may be welded, nitrogencontamination is an obstacle since it causes an increase in the tendencyfor crater cracking, serious loss of ductility and an increase in thetransition temperature. Welding also presents the problem of loss ofstrength due to recrystallization. In the handling of high strengthcolumbium alloys, recrystallization occurs between 2200 and 2800 F.,depending upon the alloy makeup. Welding involves these hightemperatures and where recrystallization as a result occurs, a loss ofapproximately 50% in tensile strength may be anticipated.

However, it has been found that by using the alloys of this invention,excellent joinder of the metals is effected and a high temperatureresistant joint is produced which is compatible with the strengthcharacteristics of the joined materials. Argon gas is utilized toprevent oxidation of the columbium and its alloys during the brazing,only moderate efforts being necessary for purification of the gaspreparatory to brazing.

The alloys of this invention are additionally useful as coatings forcolumbium and for other materials characterized by low oxidationresistance at elevated temperatures, i.e., of approximately 2000 F.

Further utility for these alloys is found in casting applications and inother areas of metal forming where adequate oxidation resistance atelevated temperatures is difiicult to achieve and maintain and whereboth structural and non-structural provisions are a requirement.

Accordingly, it is an object of this invention to provide alloys wellsuited for the brazing of columbium and columbium base alloys, whichalloys are capable of providing excellent joint strength at elevatedtemperatures.

It is another object of this invention to provide alloys of thecharacter described which do not require excessively high temperaturesfor brazing and which possess adequate ductility.

A further object is to provide alloys, as described, which do not causeexcessive erosion of columbium and columbium base alloys when appliedthereto in brazing applications.

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Yet a further object is to provide alloys suitable as protectivecoatings for preventing oxidation of materials having a highsusceptibility thereto at elevated temperatures.

Another object is theprovision of alloys adapted to cast- .ingapplications which call formaterials possessing adequate oxidationresistance at elevated temperatures.

These and other objects and advantages of this invention will becomeapparent from the following description of the alloys and theircharacteristics and the claims directed thereto.

In general the alloys of this invention include as matrix elementschromium and either or both titanium and palladium in thepercentage-by-weight ranges indicated. Each of these matrix elements ischaracterized by its com patibility with columbium and the alloysthereof. An alloying element selected from the group consisting ofgermanium, vanadium, and gold and proportioned as set forth, is added tothe matrix elements. The resulting alloys have produced brazed jointspossessing excellent joint strength at high temperatures. This brazinghas been effected without the use of extremely high temperatures.Ability of the alloys to withstand high temperatures with a minimum ofdeterioration has contributed to their further utilization as coatings,protecting against oxidation of materials susceptible thereto.Formability at practicable temperatures and the aforementioned excellenthigh temperature characteristics further dictate use of the alloys inthe area of metal forming, particularly in casting applications. It isto be understood that percentages used herein in the specification andclaims to describe ingredient proportions are percentages by Weightunless stated to be otherwise.

Chromium, as an elemental constituent common to each of the alloys hasbeen found to be quite compatible with columbium, forming a diffusionlayer which is much like that formed by titanium, but which shows moreinteraction at the interface with the brazing alloy. As used herein, thegeneral range of chromium is from about 25 to about 65% by weight of thealloy. A preferred range has been found to be from about '35 to about45%. Superior alloy compositions have been established incorporating thespecific proportions of chromium tabulated below.

Titanium has also been found to be a highly satisfactory loy matrixelement, being highly compatible with columbium and promoting formationof a narrow diffusion layer at the interface with the columbium. Itsgeneral range is from about 10% to about 67% by weight of the alloy. Apreferred range is from about 35 to about 45%. Superior alloycompositions have been formulated incorporating titanium in the specificproportions indicated.

Palladium, like chromium and titanium, serves as a matrix element. Likechromium, it has been found to be quite compatible with columbium andforms a narrow alloy layer. It enters into the alloys of this inventionin the general range of from about 5 to about 25%. Its preferred rangeis from about 10 to about 20%. Superior alloy compositions includepalladium in the quantities set forth below.

Germanium and vanadium are major alloy elements the general ranges forwhich are respectively from about 1 to about 20% and from about 5 toabout 20%. The preferred proportion for each is about 10%. Germaniumshows no obvious harmful effects upon the alloy, its ef fects any inthis respect, being masked by other alloy elements. Vanadium shows adistinct inter-granular penetration which is, however, minor. Somesolutioning of columbium occurs above 2600 F.

Gold enters into the alloy as an element which pro-, mo c i ter a i t whh is use nly a a minor element. It has been found to be quite compatiblewith columbium, forming an alloy layer and causing some solutioning ofcolumbium above 2500 F. when present in a quantity in excess of 10% byweight of the alloy composition. It is helpful in promoting ductility ofcera similar phenomenon would be found to exist for each of them.

Numerous high temperature oxidation studies of the above alloys havebeen conducted. Visual and microtain of the alloys. The range of goldentering into the 5 structural studies indicate the usefulness of thesealloys alloys of this invention is from about 1 to about 20%. A asprotective coatings for materials having low resistance preferred alloycomposition includes about gold. to oxidation at elevated temperatures.Application of Although the process for alloy formulation is subject thealloys may be accomplished by painting or spraying to variation, thealloys of this invention have for test the alloy in powdered form on thesurface of the metal purposes been formulated by mixing the elementalin- 10 to be protected and then heating the coated assembly gredientstogether in the desired proportions in powder until the powdered alloymelts to form a continuous form. The mixture is subsequently br iquettedinto a surface coating. Alloys numbers 1, 2, 3, 5, and 6 tabucompact andarc melted in a cold hearth copper crucible. lated above each showedpercent weight changes of less If ductile, the alloy is then rolled toform a foil, or than five percent after 100 hours in 2000 F. air,indicatin the alternative, broken into a powder to be used in ing theirquality as protective coatings. such form. It is the above qualities ofthe alloys of this invention As formulated herein, the alloys of thisinvention have which adapt them for use in metal forming applications.taken the powder form. Application is effected by mix- Quite obviouslysuperior corrosion resistance is offered ing the powder alloy withpolyvinyl alcohol in a slurry, at elevated temperatures and with meltingpoints as inwhich is then painted on the joint to be brazed. The alloydicated, forming is not a problem. The alloys can be is then heated to atemperature above its melting point, made up in the manner indicatedabove or in other using argon gas for protection against oxidation. Ashas conventional fashion and then formed. been earlier mentioned,moderate efforts should be made What I claim is: to purify the argongas. Herein this has been accom- 1. An alloy characterized by' itsability to withstand pl shed satisfactorily by passing the argon througha glasshigh temperatures consisting of by weight from about 35 activatedalumina dryer, a -100 F. Dry Ice-acetone to about 65% chromium, fromabout 20 to about 64% cold trap, and a closed zirconia tube filled withtitanium titanium, and from about 6 to about 15% gold. strips andoperating at 1750 F. The protection olfered 2. An alloy characterized byits ability to withstand by the argon gas is important. Shouldatmospheric conhigh temperatures consisting of by weight about 45%tamination occur it will be reflected in reduced flow and chromium,about 45 titanium, and about 10% gold. wetting of the brazing alloy. 3.An alloy characterized by its ability to Withstand For purposes of thetests the results of which are rchigh temperatures consisting of byweight from about fiected in the tabulations below, brazed lap sheartest to about 65% chromium, from about 20 to about 64% specimens weremade up using for the members to be titanium, and from about 1 to about15% germanium. joined a columbium alloy incorporating by weight 10% 354. An alloy characterized by its ability to withstand titanium and 10%molybdenum. Time at temperature high temperatures consisting of byWeight about 45% prior to testing was 1 minute. Using an A-frarne typeof chromium, about 45 titanium, and about 10% gerlap-shear tension testsetup, failure was made to occur maniurn. within 1 minute by steadilyincreasing the mechanical 5. An alloy characterized by its ability towithstand stress upon the specimen by means of a floating screw. hightemperatures consisting of by weight from about 35 Stress was measuredby means of a load link in conjuncto about 65% chromium, from about 20to about 60% tion with a strain recorder. Specimens were confinedtitanium, and from about 5 to about 25% palladium. under a protectiveargon atmosphere during heating, test- 6, An alloy characterized by itsability to withstand ing, and cooling. high temperatures consisting ofby weight from about Each of the alloys of this invention is set out inthe 40 to about 45% chromium, from about 40 to about 45% table belowwith an indication both as to the general titanium, and from about 10 toabout 20% palladium. range of its ingredients and as to the specificcomposition 7. An alloy characterized by its ability to withstand of theparticular alloy or alloys tested. Also shown are high temperaturesconsisting of by weight from about the alloy melting temperatures andthe results of shear 25 to'about 40% chromium, from about 20 to abouttests conducted at elevated temperatures with regard to titanium, fromabout 5 to about 20% palladium, each brazed joint. and from about 5 toabout 20% vanadium.

Alloy-Gen- Composition, Percent by Weight Melting It. Shear No. eralRange Temp, Strength,

or Specific F. p.s.i. Composition Or Ti Pd Ge V Gold 2,0U0 F 1 {sGcneral35-65 pec1fic 45 General 35-05 2 lSpeoific 45 Genera 35-65 3 {Specifiann40 Spec1fie.. 45 4 {grenerahuu 25-49 epee1fic 3o 5 {generaLnn 25-40pecific 35 G [General 25-40 [Spec1fic 3a During these tests, a remelttemperature rise phenomenon was observed in connection with that alloydesignated number 2 in the above tabulation of test results. That is tosay the melting temperature of this particular brazing alloy by itselfis 2540 F. However, in tests after brazing of the columbium lap shearspecimen, it was found that the alloy did not remelt at 3000 F. Although similar tests were not conducted with respect to the other of theenumerated specimens, it is believed that 8. An alloy characterized byits ability to withstand high temperatures consisting of by Weight about55% chromium, about 35% titanium, about 20% palladium, and about 10%vanadium.

9. An alloy characterized by its ability to withstand high temperaturesconsisting of by Weight from about 25 to about 40% chromium, from about20 to about 65% titanium, from about 5 to about 20% palladium, and fromabout 5 to about 20% germanium.

10. An alloy characterized by its ability to withstand high temperaturesconsisting of by Weight about 35% chromium, about 35% titanium, about20% palladium, and about germanium.

11. An alloy characterized by its ability to withstand high temperaturesconsisting of by weight from about 25 to about 40% chromium, from aboutto about 67% titanium, from about 5 to about 25% palladium, and fromabout 3 to about gold.

12. An alloy characterized by its ability to withstand high temperaturesconsisting of by Weight about 35% chromium, about 35% titanium, about20% palladium, and about 10% gold.

13. An alloy characterized by its ability to withstand high temperaturesconsisting of by weight from about to about 65% chromium, from about 20to about 67% titanium, and at least one ingredient in the rangespecified selected from the group consisting of germanium about 1 toabout 20%, vanadium about 5 to about 20%, and gold about 6 to about 20%.

14. An alloy characterized by its ability to withstand high temperaturesconsisting of by weight from about 25 to about 65% chromium, from aboutto about titanium, and at least one ingredient in the range specifiedselected from the group consisting of germanium about 1 to about 20%,vanadium about 5 to about 20%, and gold about 6 to about 20%.

15. An alloy characterized by its ability to Withstand high temperaturesconsisting of by weight from about 35 to about 45 chromium, from about35 to about 45 titanium, and at least one ingredient in the rangespecified selected from the group consisting of germanium about 1 toabout 20%, vanadium about 5 to about 20%, and gold about 5 to about 20%.

16. An alloy characterized by its ability to withstand high temperaturesconsisting of by Weight from about 25 to about chromium, at least oneingredient in the range specified selected from the group consisting oftitanium about 20 to about 65% and palladium about 20 to about 25%, andat least one ingredient in the range specified selected from the groupconsisting of germanium about 1 to about 20%, vanadium about 5 to about20%, and gold from 5 to about 20% 17. An alloy characterized by itsability to withstand high temperatures consisting of by Weight fromabout 25 to about 65% chromium, from 10 to about 67% titanium, and fromabout 10 to about 20% palladium.

References Cited in the file of this patent UNITED STATES PATENTS1,471,326 Copland Oct. 23, 1923 2,169,193 Cornstock Aug. 8, 19393,063,835 Stern Nov. 13, 1962 FOREIGN PATENTS 373,725 Germany Apr. 14,1923 714,820 Germany Dec. 8, 1941

1. AN ALLOY CHARACTERIZED BY ITS ABILITY TO WITHSTAND HIGH TEMPERATURESCONSISTING OF BY WEIGHT FROM ABOUT 35 TO ABOUT 65% CHROMIUM, FROM ABOUT20 TO ABOUT 64% TITANIUM, AND FROM ABOUT 6 TO ABOUT 15% GOLD.